Auto-balancing gets complicated when handling more than two supercapacitor cells. A new board from Advanced Linear Devices combats this with the ability to balance up to six supercapacitors of any size.

Advanced Linear Devices Inc. (ALD) recently released the SABMB6, a new six-channel PCB performing supercapacitor automatic balancing (SAB) operation for over-voltage protection. The board targets 12-V battery applications where six 2 V cells are being increasingly stacked in series or parallel.

The SABMB6 board comes populated with three ALD9100XX SAB MOSFETs that automatically balance up to six connected supercapacitor cells by equalizing the leakage current of each cell.

The board allows a supercapacitor cell’s charging and discharging currents to pass through the cells themselves directly while bypassing the SAB MOSFETs mounted on the board with near-zero additional leakage current. And that prohibits additional power dissipation used by the circuitry, which in many cases exceeds the supercapacitor energy burn caused by leakage currents.

SABMB6 can balance up to six supercapacitors connected in stack. Image courtesy of ALD.

The new board joins ALD's joins two- and four-channel PCBs, the SABMB2 and SABMB16, respectively. These multi-channel PCBs can be cascaded with a mix-and-match configurability to automatically balance supercapacitor cells in stacks. The board measures 15.24 mm x 40.64 mm and is made from RoHS-compliant FR4 material and can operate at the industrial temperature range of -40 °C to +85 °C.

The SABMB6 board also offers the option of installing the reverse-biased external power diodes—Schottky rectifiers—across each SAB MOSFET to clamp the surge current transients. The SABMB6 board is also available as a blank PCB so that designers can insert their own SAB MOSFETs on the board.

The plug-and-play PCB bypasses the need for a significant amount of design work; all that's required is for an engineer to mount the PCB and wire the appropriate connections from the SABMB6 board to the respective supercapacitor nodes. SABMB6, a high-voltage supercapacitor balancing PCB, allows system engineers to test, evaluate, and prototype over-voltage protection in power systems and then enter production volume.

A PCB Built Around SAB MOSFETs

The high-voltage supercapacitors are increasingly used to address the energy storage and power backup needs in applications such as datacenters, energy harvesting, transportation, and industrial automation. However, over-voltage is a major cause of failures in supercapacitors. To ensure that supercapacitor cells connected in stacks of two or more have a reliable over-voltage protection, SAB MOSFETs are installed on the board.

The SAB MOSFETs balance each supercapacitor cell through low levels of leakage current without exposing cells to charge and discharge voltage levels. Here, MOSFETs save supercapacitor leakage current and associated power dissipation by lowering the operating bias voltage of the leakier of the two supercapacitors connected in stack.

This is how the SAB MOSFETs like ALD9100XX automatically balance supercapacitor cells in the stack. Image courtesy of ALD.

As compared to other passive and active balancing methods, including op-amp-based techniques, SAB MOSFETs ensure that the additional leakage current contributed by the PCB is approximately zero. Or it’s not more than a small percentage of the highest supercapacitor cell’s leakage current in the stack.

A growing number of applications are now using multiple supercapacitor cells in modules in order to meet the energy storage needs of higher voltage systems. Here, two or more supercapacitor cells in applications like high-current energy storage for industrial systems demand safe voltage balancing to extend the product life of stacked supercapacitors.

What's your experience with supercapacitors? What applications would you look to a SAB MOSFET board for? Let us know in the comments below.